1. Field of the Invention
This invention relates to a new type of photographic color coupler, photographic color materials containing the same, and, further, to a method of image formation using such photographic color couplers.
2. Description of the Prior Art
As is well known in the art, dye images can be formed by imagewise exposure of a silver halide photographic material followed by color development whereby the oxidation product of an aromatic primary amine developing agent reacts with a dye forming coupler.
Generally speaking, this dye image method is based on the subtractive color reproduction principle, with cyan, magenta and yellow dye images, each of which is in a complementary relationship to red, green and blue light, respectively, being produced. For example, cyan dye images are generally produced from couplers comprising phenol or naphthol derivatives. The reaction between the coupler and the color developing agent takes place at the active sites of the coupler. One mole of a so-called "four-equivalent coupler" in which all of the active sites are substituted with hydrogen atoms theoretically requires on a stoichiometric basis 4 moles of silver halide as developing nuclei. On the other hand, two-equivalent couplers are known which have substituents releasable as anions at the active sites and which require only 2 moles of silver halide as developing nuclei. Accordingly, by use of 2-equivalent couplers, the amount of silver halide in the photographic coating can be generally reduced and, hence, the coating thickness thereof can be reduced. This, in turn, enables the processing time to be decreased and simultaneously results in the sharpness of the resulting dye images being advantageously improved. A variety of such coupling releasable groups are known including, for example, the sulfonamido groups set forth in U.S. Pat. No. 3,737,316, the imide groups set forth in U.S. Pat. No. 3,749,735, the sulfonyl groups set forth in U.S. Pat. No. 3,622,328, the allyloxy groups set forth in U.S. Pat. No. 3,476,563, the acyloxy groups set forth in U.S. Pat. No. 3,311,476, the thiocyano groups set forth in U.S. Pat. No. 3,214,437, the isothiocyanate groups set forth in U.S. Pat. No. 4,032,345, the sulfonyloxy groups set forth in U.S. Pat. No. 4,046,573, the thiocarbonyloxy groups set forth in Japanese patent Application (OPI) No. 51939/1977 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application"), the aralkenylcarbonyloxy groups set forth in Japanese Patent Application (OPI) Nos. 39126/1978 and 39745/1978, the S-substituted monothiocarbonyloxy groups set forth in Japanese Patent Application (OPI) No. 45524/1978, the propionyloxy groups set forth in Japanese Patent Application (OPI) No. 47827/1978, the ##STR2## groups set forth in U.S. Pat. No. 4,072,525, and the substitued alkoxy groups set forth in U.S. Pat. Nos. 3,227,551 and 4,052,212 and Japanese Patent Application (OPI) Nos. 120334/1975, 18315/1977, 90932/1977 and 52423/1978.
Further, if the coupler contains a suitable type of coupling releasable group, for example, one which forms a diffusible dye structure, such a coupler, referred to as a diffusible dye releasing coupler, such can be employed in a diffusion transfer process in which the released dye is used to provide a dye image in an image receiving layer. Diffusible dye releasing couplers are described in, for example, U.S. Pat. Nos. 3,227,550, 3,765,886, U.S. Defensive Publication T900,029, British Pat. No. 1,330,524, etc. Besides, certain 2-equivalent, colored couplers exhibit a masking effect to correct undesirable absorptions of dyes as described in, for example, Japanese Patent Application (OPI) No. 26034/1976.
Furthermore, 2-equivalent couplers, which are referred to as development inhibitor releasing couplers, are known. Since these couplers release compound suppresses or inhibits development, these couplers are quite effective in improving image graininess, gradation control as well as improving color reproduction characteristics. These couplers can also be used in a diffusion transfer process because they affect a layer adjacent the layer in which they are present. Examples of these couplers are described in U.S. Pat. No. 3,227,554, Japanese Patent Application (OPI) No. 122335/1974 and German Patent Application (OLS) No. 2,414,006.
Since a 2-equivalent coupler has a wider range of applications as compared with a 4-equivalent coupler, the photographic industry tends to use this type of coupler more frequently.
However, most prior art 2-equivalent cyan dye forming couplers have certain disadvantages including insufficient coupling reactivity, the tendency to form color stains, poor dispersion stability which causes difficulties during coating, lack of storage stability, insufficient fastness of the resulting dye image in the finished product, etc.